An 1861 map showing the distribution of the slave population in the South helped illustrate the cause of the Civil War — the South’s reliance on slavery. Library of Congress

The debate dominated the discussion for two days in the middle of 1787′s Constitutional Convention, raising awkward questions about race and personhood that foreshadowed a bloody conflict decades later.

How would the new nation count slaves in its first census? States with larger populations faced a mixed bag of benefits: More people would mean more political representation, but also a higher tax burden. The debate was fraught on multiple levels, not the least because of the complicated issues that arose from defining other humans as property.

Massachusetts delegate Nathaniel Gorham noted the convoluted logic of his counterparts from slave-owning states.

These delegates liked to argue that blacks were inferior to freemen when the issue of taxes came up, he said, according to James Madison’s notes of the day. But when the question of political representation came up, “We are assured they [slaves] are equal to freemen.”

A compromise was struck to address the issue: slaves would be counted in the census, but they would be given weight as three-fifths of a person for financial and political purposes. And that compromise continued until the end of the Civil War and the passage of the 14th Amendment, which granted citizenship to all people born or naturalized in the United States.

Now, more than 200 years after its creation, another racially fraught debate about the census draws focus to its meaning and historical legacy. The Trump administration’s push to add a question about citizenship to has unfolded in dramatic fashion, though President Donald Trump announced Thursday that he would back down from his attempts.

The debate about citizenship is distinct, driven by the demographic and political concerns of the moment. But there is a throughline.

“It’s always about more than counting,” said Susan Schulten, chair of the history department at the University of Denver and an expert on 19th-century America. “There’s always an agenda behind the count . . . What you’re seeing is the census as an instrument of political power.”

The compromise arraigned at the 1787 convention was enshrined in the Constitution.

“Representatives and direct Taxes shall be apportioned among the several States . . . determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons,” it read.

The first census asked for the name of the head of each household, as well as the number of male whites under 16 and over 16 – information to prepare in case of another war – the number of free female whites, free other persons and slaves. The vast majority of Native Americans lived separately from the settlements established by white Americans at the time and therefore were not a very large part of the count.

Madison’s notes from the convention demonstrate the fallacies in the classification of people as property. Many delegates tried to parse the ways in which slaves were both property – Virginia delegate George Mason called them a “peculiar species of property” – and not.

Others wondered why if slaves were property they would be included at all, when other property was not a part of the Census. Some delegates admitted that the logic was thin.

“Are they admitted as citizens – then why are they not admitted on an equality with white citizens? Are they admitted as property – then why is not other property admitted into the computation?” Pennsylvania delegate James Wilson asked, according to Madison’s notes.

But those contradictions wouldn’t be smoothed out at the convention. That would have to come later. And that was where the compromise originated.

“These were difficulties, however, which [Wilson] thought must be overruled by the necessity of compromise,” Madison noted.

The decision to include slaves was hugely consequential.

It substantially increased Southern political representation, as historians such as Garry Wills have argued, potentially enough to tip the balance in close political battles for decades.

“Without the federal ratio as the deciding factor in House votes, slavery would have been exuded from Missouri, Jackson’s Indian removal policy would have failed,” Wills argued in his 2003 book ” ‘Negro President’: Jefferson and the Slave Power.”

The presidency was held by slave owners for 50 years, and the speakership of the House, 41, while 18 Supreme Court seats out of the 31 before 1850 were held by slave owners, Wills noted, citing a survey that showed that half of the highest federal officeholders were southerners, while the North had almost twice the free population as the South.

“The federal ratio, and its ripple of side effects, had a great deal to do with the fact that for over half a century, right up to the Civil War, the management of the government was disproportionately controlled by the South.”

Those statistics had other effects as well, increasing the social understanding of slavery that eventually lead to the Civil War.

In 1807, the United States banned the importation of slaves, leading some to think that the slave population would eventually die out – what was referred to as following “the fate of the Indians,” said Margo Anderson, a professor emeritus at the University of Wisconsin at Milwaukee and an expert on race issues in the census.

But the census showed the opposite was the case – the slave population continued to grow, from 650,000 in 1790, to 2 million in 1830, to 4 million in 1860 on the eve of the Civil War, about a third of the South’s population the whole time.

“Once Americans realized that, particularly in the North, they built an abolitionist movement,” Anderson said. “They were thinking, ‘We have to get rid of this’ – not by natural demographic pattern but by legal abolition. And that’s what got us the Civil War.”

A 1861 map based on census data that showed the concentration of slaves became a powerful visual illustration of reasons that animated the Civil War – the South’s reliance on slavery, Schulten said.

“It is treated as an incredible document and it is a favorite of Lincoln because it visualizes for the whole Union front and leadership just how tied to slavery secession really is,” she said. “Once it was visualized, that became a very powerful tool to demonstrate that slavery had driven the way.”

C. Matthew Snipp, a sociology professor at Stanford University and a former member of the Census Bureau’s Racial and Ethnic Advisory Committee, said in an interview that the census has always been a reflection of contemporary understandings of race.

One thing that is different now is how hastily the citizenship question appeared to have been proposed, Snipp said. He said he had spoken to some contacts in the Census Bureau.

“To a person they’re fairly appalled because it bypasses the processes, it’s going to gum up the system, they were completely blindsided by this, and it’s a bad idea from beginning to end,” he said. “I think everybody is acutely aware that this is a potentially damaging measure that this is going to result in a census that is not going to be the quality that they had planned for and is probably going to cost more money.”